I dunno, I could see genius as making one susceptible; but also more able to endure the strain of less than psychotic mania for some time. Or they may both be facilitated by a similar atypical brain structure or chemistry; thus they may both occur, but neither causes the other.

On the exaggeration thing; I'd like to make a counterpoint, if we just look at IQ type intelligence, its not hard to end up in a job where it is very easy to note, objectively, something interfering with your cognitive function. Particularly, complex, mathematical/modelling tasks. When the same task goes from 3 minutes to 7 minutes; consistently, you know something is up. Or at least I did. I've always managed my stress levels very carefully, avoided all recreational substances, never been to a party, bar, and rarely even a restaurant or movie. So I never had that episode that would lead to hospitalization... the scary reality, is that in one or two more iterations, if I'd broken while depressed, I'd have completed a suicide without saying a word to anyone; or manic, would just have ended up as a typical sport, "grey hair dies doing something far beyond his capacity".

I do think they set the bar too low on using the term, "genius" though. 3rd SD of whatever type of smarts is certainly potent enough to make a substantial difference in performance; but having some contact with 5th SD people, I can assure you, the difference is staggering.